1. Field of the Invention
Embodiments of the invention generally relate to methods for depositing materials within a feature, and more specifically to methods for depositing a seed layer prior to filling a contact plug with a copper-containing material by an electroless deposition process.
2. Description of the Related Art
Reliably producing nanometer-sized features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) of semiconductor devices. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of this technology require precise processing of high aspect ratio features, such as vias and other interconnects. Reliable formation of these interconnects is very important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates.
As circuit densities increase, the widths of vias, apertures, trenches, contacts, and other features, as well as the dielectric layers between them, decrease to nanometer dimensions, whereas the thickness of the dielectric layers remain substantially constant. Therefore, the aspect ratios of the features increase with the duration of time. Many traditional deposition processes have difficulty filling nanometer-sized structures where the aspect ratio exceeds 4:1, and particularly where the aspect ratio exceeds 10:1. Therefore, there is much effort directed at the formation of substantially void-free, nanometer-sized features having high aspect ratios.
Currently, copper and copper alloys have become the metals of choice over aluminum for nanometer-sized interconnect technology. Copper has a lower electrical resistivity (about 1.7 μΩ-cm compared to about 3.1 μΩ-cm for aluminum), a higher current carrying capacity, and significantly higher electromigration resistance than aluminum. These characteristics are important for supporting the higher current densities experienced at high levels of integration and increased device speed. Further, copper has a good thermal conductivity and is available in a highly pure form.
Electroless deposition processes, unlike electroplating processes, utilize autocatalyzed chemical deposition instead of an applied current to induce chemical reduction. An electroless deposition process typically involves exposing a substrate to a solution by either immersing the substrate into a bath or spraying the solution over the substrate. An electroless deposition process of a copper-containing material within nanotechnology requires a surface capable of electron transfer for nucleation of the copper material to occur over the surface, such as a catalytic seed layer. Non-metallic surfaces and oxidized surfaces are examples of surfaces which usually do not support electron transfer. A barrier layer containing tantalum, tantalum nitride, titanium, or titanium nitride may provide for a poor nucleation surface to a subsequently deposited copper-containing material. Native oxides that are easily formed on the barrier layer may cause the poor nucleation.
An electroless deposition process may utilize a seed layer as both a catalytic surface as well as an adhesion surface. A seed layer may serve as a surface capable of electron transfer during an electroless deposition process to deposit copper-containing material. However, if there are discontinuities in the seed layer across the surface, then a subsequently deposited copper-containing layer may not form uniformly to cover the seed layer. A seed layer may also function as an adhesion layer to the underlying barrier layer or contact surface. For example, a copper layer deposited on a tantalum nitride barrier layer without an intermediate adhesion seed layer is easily peeled away during a standard tape test.
Therefore, there exists a need to deposit a seed layer within a feature on a substrate surface prior to filling the feature with a copper-containing material by an electroless deposition process, wherein the seed layer adheres the copper-containing layer to the underlying surface and the copper-containing layer is free of defects.